Phosphatidylserine acyl groups

Glycerophospholipids contain a glycerol skeleton to which two fatty acids are esterified saturated fatty acids occupy mostly sn-position 1, whereas unsaturated fatty acids are mainly present on sn-position 2. The third hydroxyl is linked to a phosphate group to which an organic base is mostly esterified (Fig. 1). The most important components of soybean lecithin are phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Phosphatidic acid (PA) may become important due to the presence of phospholipase D this enzyme slowly converts PC into PA in vegetable lecithins. Phosphatidylserine (PS), phosphatidylglycerol (PG), and lyso-phosphatidylcholine (LPC) are known as minor components lysophospholipids contain only one acyl group per molecule. Besides, ether phospholipids occur in which one or both fatty acyl... 

Figure 35.11 Phosphatidic acid. This is the parent molecule of the phospholipids. Like triacylglycerol, it has a glycerol backbone but instead comprises two fatty acyl groups and one phosphate group. When this phosphate reacts with OH groups of compounds such as choline, ethanolamine, serine or inositol, phospholipids are formed known as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol (Chapter 36).

Fig. 1.9 Structures of charge neutral (phosphatidylcholine) and acidic (phosphatidylserine) phospholipids together with the moderately lipophilic and basic drug chlorphentermine. The groupings R1 and R2 refer to the acyl chains of the lipid portions.

Isopropylideneglycerol is treated successively with phosphorus oxychloride and Af-phthalylserine. Hydrolysis of the ketal and the phospho-monochloride groups then yields glycero-3-phos-phoryl-A -phthalylserine as the barium salt after neutralization with barium hydroxide. Acylation with an excess of acid chloride then furnishes the desired phosphatidylserine. In addition, the acylation can be accomplished in a stepwise manner to give mixed-acid phosphatidylserines (Shvets etal., 1967). 

The parent molecule of the phospholipid family is phosphatidic acid (Fig. 36.1). It consists of a glycerol backbone to which are esterified two fatty acyl molecules (palmitic acid is shown here) and phosphoric acid. The latter produces a phosphate which is free to react with the hydroxyl groups of serine, ethanolamine, choline or inositol to form phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine or phosphatidylinositol, respectively. 

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